1. Field of the Invention
The present invention relates to a wireless distance measurement system and a wireless distance measurement method that measure the distance between a wireless communication terminal apparatus and a base station apparatus using UWE (Ultra Wide Band) communication scheme.
2. Description of the Related Art
One of high-speed wireless transmitting techniques includes the UWB communication scheme. The UWB communication scheme is a technique of performing ultrahigh speed wireless communication using a pulse signal sequence formed with a pulse signal synchronized with a timing of a predetermined period. An example of UWB communications is known that communication is carried out using a pulse signal sequence formed with extremely short pulse signals having a pulse width of 1 nanosecond or less without using carrier waves.
Meanwhile, for example, Patent Document 1 discloses a distance measurement technique, in which a base station apparatus (hereinafter “base station”) measures the distance to a wireless communication terminal apparatus (hereinafter “terminal”). The distance measurement technique disclosed in Patent Document 1 uses differences between times of arrival of signals received at a terminal using 3 or 4 base stations.
FIG. 1 shows the positioning system disclosed in Patent Document 1. Referring to FIG. 1, the positioning system has a plurality of base stations 11, 12 and 13, and calculation server 14, and, base station 11 to 13 and calculation server 14 are connected by wired network 15. This positioning system is directed to calculating the position coordinate of terminal 10.
In the system disclosed in Patent Document 1, positioning of a terminal is conducted using propagation time differences between measurement signals transmitted and received between the terminal and the base station. To find the absolute time of signal propagation, it is necessary to synchronize the clock of a terminal and the clock of the base station. However, in a general wireless communication system, a terminal and the base station are not synchronized, and therefore it is not possible to conduct positioning (i.e. TOA: Time Of Arrival) using absolute propagation time. However, when a plurality of base station clocks are synchronized, it is possible to find differences of times a measurement signal takes to arrive at the base stations, and it is possible to conduct positioning (i.e. TDOA: Time Difference Of Arrival) using relative propagation time (propagation time difference) Patent Document 1: Japanese Patent Application Laid-Open No. 2004-242122
However, with the positioning system disclosed in above Patent Document 1, the differences between propagation times a measurement signal takes to arrive at a plurality of base stations are used for measurement, and therefore, it is necessary to synchronize the clocks of a plurality of base stations. Consequently, it is necessary to connect the base stations with a cable, or provide a reference station to make clocks to be synchronized besides the base stations for measurement. Further, to measure the distance to a terminal from differences of propagation times for a plurality of base stations, it is necessary to keep the relative position relationships between a plurality of base stations as data, and there is a problem that the positions of the base stations should be measured in advance.